1. Field of Invention
The present invention relates to a manufacturing filed of punch dies, and more particularly to a pressing and stripping apparatus for a punch die and a push rod thereof.
2. Description of Related Arts
A punch die for a punch press generally comprises of a convex-concave die, a pressing and stripping plate, a pressing and stripping functional element, a fixing plate, a liner plate, guide pins, a base, and iron pads. The pressing and stripping functional element of the punch die is often provided within the die, while a handful of bending dies are hung at outer side of the lower base. They have a one-to-one configuration and are not interchangeable. Current pressing and stripping functional elements are all resilient elements such as casting polyurethane, rubber and metal springs, or nitrogen springs; wherein the features of the casting polyurethane, rubber and metal spring are that the initial pressure is zero and the pressing force is in direct proportion with the amount of compression. Therefore, the spring should be pre-pressed with an amount of compression being 5-8% of the length of the spring in order to obtain an initial pressure. The amount of compression of every type of resilient element is predetermined, for example, the effective amount of compression for a commonly used heavy load spring SWB (A spring serial number of a Japanese company MISUMI) in a punch die is 20% of the spring length. This means that the amount of compression in use with the SWB spring is about 12-15% of the length, so that the length of the SWB spring usually is larger than 50 mm. The nitrogen spring is a single piston rod pneumatic cylinder with preset compressed nitrogen. The advantage of a nitrogen spring is that the initial pressure is relatively large, but its length is often larger than 100 mm. The die should be designed to have a relatively large thickness so that these pressing and stripping functional elements can be installed in the upper and lower mould of the die. As a result, the die is bulky in size and it is a large waste of high quality steel materials.
With the development of the material living standard of the human beings, the upgrading and replacing of the products becomes more and more frequent. The production life of a single machine type of many mechanical and electrical products such as CD players, VCD players, DVD players, and TV sets has decreased from over a million in the 80s and 90s to tens of thousands at present. Accordingly, dies for manufacturing the products also have to be upgraded and replaced frequently. According to international convention, dies for mechanical and electric products which have stopped production should be preserved carefully for five to seven years in the case that there is a need to produce a few and a handful of spare parts. Therefore, during the past ten years many factories have stored large quantities of dies which have been placed out of service. Accompanying with the more and more increasing requirement for a low carbon economy as well as for energy-saving and emission-reduction; simplifying the structure of the die, and reducing the manufacturing period and manufacturing cost of the die while ensuring that the function of the die in use will not change have become a new trend for the development of dies in the future.